This invention relates to a process for rapidly and accurately dispensing fluids and to an apparatus useful for performing this process.
In industrial practice, there are many applications in which, during the production of a product, two or more fluids of differing densities and of differing viscosities must be dispensed, wherein the quantities of the individual components vary over a wide range. Examples are the production of fragrances or flavors, colorant mixtures, adhesives etc. Another example is the production of a polyurethane reaction mixture on the laboratory scale. In complex systems, from 5 to 50 different components each having a viscosity which may vary from 0.1 to 400,000 mPa·s, must be dispensed in quantities which may vary over a wide range (e.g., from 0.001 to 1000 ml or from 0.001 to 1000 g).
In practice, the individual components are dispensed volumetrically.
In such applications, automatic pipettes/fluid handlers are used for very small quantities of relatively low viscosity substances, while lobe pumps or positive-displacement pumps (membrane, piston or gear pumps) with positive displacement pistons for batch displacement are used for larger quantities. While this principle generally functions satisfactorily for low viscosity fluids, high viscosity fluids, in particular those involving high viscosity, resinous components, cannot be dispensed using such methods. In the transitional range, i.e. in medium viscosity fluids, dispensing errors of greater than 5% readily occur. In particular, each component must have a dedicated dispensing pump, which increases equipment costs. Depending upon the quantity and viscosity of the individual components, dispensing pumps of differing sizes and powers, each having different functional characteristics (i.e. dispensing accuracy) must be used.
The use of mass flowmeters also presents major disadvantages because the large number of flowmeters required creates considerable complexity in controlling the dispensing process.